Or (d) there are nocturnal or cave dwelling beings that have a preference for the dim and dark and this is the part of the bar where they hang out. Or (e) the owners don't care about what the non-patron areas look like so they saved money on buying equipment. Or (f) any combination or all of the above.... you get the idea. Lots of different reasons for having a place that isn't made specifically for the PCs. I don't think most players will be thinking about these sorts of things, so they'd make for a good twist on the usual expectations.

In-movie, this feels like quite the jump in atmosphere from Finn getting found out as the traitor, and I'm not sure what to think of that. Maybe there's a scene cut that's not a part of the comic? Rey doesn't seem to be moving that quickly or cautiously as evidenced by the walking down the middle of this hallway with the bright overhead lights. And BB-8's following not exactly close behind probably making a racket thunking down the stairs.